Marketable Securities - (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2012
securities
Jun. 30, 2011
Jun. 30, 2012
securities
Jun. 30, 2011
commercial_mortgage-backed_securities
Investments, Debt and Equity Securities [Abstract]        
Number of commercial mortgage backed securities sold (in securities)       6
Proceeds from sale of marketable securities     $ 0 $ 82,061
Marketable Securities, Gain (Loss) $ 0 $ 7,728 $ 0 $ 15,587
Number of commercial mortgage backed securities (in securities) 0   0